When the driving stability of a vehicle is being controlled, the driving behavior of a vehicle is influenced in such a way that the driver can maintain better control of the vehicle in critical situations. A critical situation is here an unstable driving state in which in an extreme case the vehicle does not follow the driver's prescriptions. The function of driving stability control is therefore to cause the vehicle to adopt the driving behavior desired by the driver within the physical limits in such situations.
The term driving stability control can be used to cover multiple principles for influencing the driving behavior of a vehicle by means of predefinable braking torques at individual wheel brakes and by intervening in the engine management system of the drive engine. This involves an anti-slip brake system (ABS), which is intended to prevent individual wheels locking during a braking process, a traction control system (TCS) which prevents the driven wheels from spinning, an electronic braking force distribution system (EBFDS), which controls the ratio of the braking forces between the front axle and rear axle of the vehicle, a tilt control system (ARP) which prevents the vehicle from tilting about its longitudinal axis, and a yaw moment control system (ESC), which ensures that there are stable driving states when the vehicle yaws about the vertical axis. During yaw moment control, an additional yaw moment is built up, by selectively braking individual wheels, in order to reduce the yaw rate difference between the measured actual yaw rate and the setpoint yaw rate which is determined on the basis of a vehicle model, wherein the slip angle is frequently also controlled.
Previously known systems for controlling the driving stability of a vehicle provide for fixed distribution of the stabilizing additional yaw moment about the vertical axis between the front and rear axles during an oversteering situation, wherein a braking torque is generated mainly at the front axle. The asymmetrical braking torque at one wheel of the front axle can lead here to an undesired reaction on the steering.
In vehicles with a hydraulic brake system, braking torque is built up independently of the driver by actuating a hydraulic pump and suitably actuating solenoid values. This has the disadvantage that noise which disturbs the driver is produced.